The present invention relates to a semiconductor device and to a method for fabricating the same. More particularly, it relates to a semiconductor device using copper interconnections and low dielectric constant films and to a method for fabricating the same.
With the recent trends toward the higher integration and smaller chip size of a semiconductor integrated circuit, the provision of miniaturized and multilayered interconnections has been promoted. A reduction in the spacing between the interconnections increases an interconnection resistance and a capacitance between the interconnections so that a signal delay resulting from the interconnection resistance and the capacitance between the interconnections becomes no more negligible. To pursue the miniaturization of the semiconductor integrated circuit, therefore, it is necessary to reduce a parasitic capacitance occurring between the interconnections. To reduce the parasitic capacitance between the interconnections, it is necessary to reduce the resistivity of each of the interconnections or the specific dielectric constant of an interlayer insulating film.
In a 0.13 μm gate length device, the replacement of an aluminum (Al) interconnection with a copper (Cu) interconnection formed by using a damascene process has been undertaken to reduce the resistivity of the interconnection. The use of the Cu interconnection formed by using the damascene process can reduce the resistivity of the interconnections to a level corresponding to about ⅔ of that of the conventionally used interconnection. In the Cu interconnection, however, Cu atoms are diffused rapidly into an insulating film, such as a silicon oxide film (SiO2 film), so that the Cu atoms has the possibility of entering a transistor and causing the breakdown of the transistor. When the Cu atoms are diffused into a space between the interconnections and an unexpected cross-linked structure is formed therein, the phenomenon of an undesirable lowering of the breakdown voltage between the interconnections or the like may occur. Therefore, it is necessary to provide a barrier film for preventing the diffusion of the Cu atoms around a Cu film in the Cu interconnection.
To compose a barrier film, it is common practice to use a conductive barrier film (hereinafter referred to as a barrier metal film) made of tungsten nitride (WN), tantalum nitride (TaN), or titanium nitride (TiN) and covering the bottom and side surfaces of the Cu film and an insulating barrier film made of silicon nitride (SiN), silicon carbide (SiC), or the like and covering the upper surface of the Cu interconnection. Since a Cu interconnection is more difficult to form by an etching process than an Al interconnection, the formation of the Cu interconnection has been performed by a damascene process.
On the other hand, the replacement of a SiO2 (with a specific dielectric constant of 4.2) film with a fluorine-containing silicon oxide film (with a specific dielectric constant of 3.7) has been undertaken to reduce the specific dielectric constant. In a 90 nm device or later, an insulating film (low dielectric constant film) with a specific dielectric constant lower than that of the fluorine-containing silicon oxide film is needed so that the use of a carbon-containing silicon oxide film, a coating-type organic polymer, or the like having a specific dielectric constant reduced by substituting the terminal of silicon in a SiO2 film with an alkyl group (e.g., —CH3 group) and providing porous and lower-density SiO2 has been examined. An example of a semiconductor device using a Cu interconnection and a low dielectric constant film and a fabrication method therefor is disclosed in, e.g., Japanese Laid-Open Patent Publication No. 2003-309174.